Journal of Mechanics in Medicine and Biology

Pedicle screws have been widely used for the treatment of spinal diseases, but improper screw placement is not uncommon and may lead to neurovascular injuries and reduced screw fixation strength. This study aimed to investigate the feasibility of using real-time screw insertion torque monitoring to prevent screw penetration. Commercially available synthetic L4 vertebrae were divided in to seven test groups based on different screw placements. Screw insertion torque and maximal pullout strength were compared among groups. The results indicated that the insertion torque gradually increased when the screw tip was within vertebral cancellous bone without penetration. However, an instantaneous decrease of torque value was observed once the screw tip penetrated the cortex wall. When compared to the control group, higher pullout strength was found for the groups with medial cortex penetration. However, vertebrae with medial cortex penetration may lead to the concern of neurovascular damage. Meanwhile, lower pullout strength was found for the groups with lateral cortex penetration and end-plate penetration, which may lead to the concern of screw loosening. We concluded that pedicle screw penetration can be judged using real-time screw insertion torque monitoring during surgery, which may aid surgeons in avoiding neurovascular injury and reduction of screw fixation strength.

Purpose: This study investigated the effects of the contact percentage (BMC%) of three-dimensional (3D) bone-to-miniscrew specimens in relation to host bone quality on initial miniscrew stability. Furthermore, their correlations were evaluated.

Methods: Orthodontic miniscrews (1.6mm in diameter and 11mm in length) were inserted into four types of artificial bones to measure the maximum insertion torque value (ITV). The miniscrew and artificial foam bone specimens were also scanned using microcomputed tomography, and the obtained images were imported into Mimics software to reconstruct the 3D models and calculate the BMC%. The Kruskal–Wallis test, Wilcoxon rank-sum test with Bonferroni adjustment, and Spearman correlations were applied for statistical and correlation analyses.

Results and Conclusions: Inserting the orthodontic miniscrew into artificial foam bone exhibiting higher bone quality resulted in higher maximum ITV and BMC%. The initial implant stability, quantified using ITV, was strongly positively ($r=0.97$) and correlated with BMC%, as measured from microcomputed tomography images.

Total ankle replacement (TAR) surgery is one of the useful methods to treat ankle arthritis. Selective laser melting that is an additive manufacturing (AM) technique has made it possible to fabricate orthopedic implants. However, there are rare studies to analyze AM implants using finite element method. Thus, the purpose of this study was to investigate the effect of the various porous designs with three types of tibial shapes for five ankle postures using three-dimensional (3D) human lower extremity models. The variable-axis-mobile-bearing (VAMB) TAR models were developed in one solid TAR design and three porous TAR designs on the tibial and talar components. Additionally, three shape designs (curved, flat, and tilted) of the tibial component were also evaluated. Each TAR design was assembled on the human lower extremity model with standing, inversion, eversion, plantar flexion, and dorsiflexion ankle postures. The results showed that there was a minor effect among the solid and porous TAR designs on the implant stability, the bone stress, and the implant stress. However, those performances in the plantar flexion were significantly reduced compared to that in the other ankle postures. Although the porous TAR designs have a higher risk of implant failure and bone breakage, it may have better bone-implant bonding ability. This study could help engineers and surgeons to understand the design rationale and biomechanics of AM-based TAR devices.

A rotationally unstable pelvic fracture can lead to loss of function and limit moving ability. Immediate fracture fixation is needed for patients with the pelvic fractures. However, it may be difficult to evaluate different surgical strategies for the fracture treatments due to variations in patients’ anatomies and surgical techniques. Thus, the purpose of the present study was to analyze the biomechanical performances of the intact, injured, and treated pelvises based on different physiological movements of the spine using finite element method. Three-dimensional musculoskeletal finite element models of the spine-pelvis-femur complex were developed. The intact pelvis, the rotationally unstable pelvis, and six types of pelvic fixation techniques were analyzed. Additionally, seven types of physiological movements of the spine were also considered. The results showed that the posterior iliosacral screws combined with lower and anterior plate (PIS-LAP) had good fixation stability, lower plate stress, and lower pelvic stress. However, the PIS-LAP increased the stress of the posterior iliosacral screws. The right lateral bending, left lateral bending, and flexion significantly affect all the biomechanical performances compared to the other physiological movements of the spine. The present study can provide engineers and surgeons with the understanding of the biomechanics of various fixation techniques during different physiological movements for the treatment of rotationally unstable pelvic fractures.

Most caregivers have low back pain which results from frequent care activities such as assistance motion that supports transfer and standing-up. Various parameters are associated with the caregiver’s lumbar load. In this study, we focus on the foot position of the caregiver as one of the subjective adjustable parameters. This study aimed to analyze the relationship between foot position and stresses of the L4–L5 joint as lumbar load during supporting standing-up via musculoskeletal simulation. The musculoskeletal model was tasked with simulating supported standing-up motions based on a specific pelvic position and angular variation of each joint. The anterior foot (left foot) was fixed, and the posterior foot (right foot) was moved to three backward positions and three rightward positions, thus obtaining nine posterior foot positions. Compressive, anteroposterior shear, and lateral shear stresses of the L4–L5 joint were compared for nine foot positions. The results showed that as the anteroposterior distance and lateral widths between both feet increased, the average value of compressive/shear stress of the L4–L5 joint during motions decreased. From our findings, we hypothesized that the foot position may reduce the lumbar load and prevent low back pain.

The ever-increasing incidence of end-stage renal disease (ESRD) has already become a major burden to health budgets and a threat to public health nationwide in Taiwan. According to the United States Renal Data System Annual Data Report in 2015, the prevalence and incidence of ESRD in Taiwan are the highest in the world. Moreover, for the population of 82 thousand ESRD patients receiving hemodialysis treatments, the total cost is up to NT$34.2 billion annually out of the National Health Insurance (NHI) program budget. This project is to design a wearable medical device which can measure and monitor the fluid dynamics of the dialysis access using sensor of phonoangiography (PAG) for exploring vascular pitch pattern and sensor of Photoplethysmography (PPG) for estimating the flow volume as a double checking of the AV access condition. We use arteriovenous access (AVA) stenosis detector based on phonoangiography technique and autoregressive model to detect access stenosis and simultaneously estimate the status of AVA life cycle by tracking and obtaining changes in frequency spectra domain. It helps hemodialysis patients to be aware earlier of the dysfunction of AVA and reminds them to make a return visit. The purpose of the complement deployment of vital sign sensors is to improve the prognosis and optimize overall health by providing analysis of physiological signals, including water content index, pulse oximetry, and blood pressure at the same time. With these sensors, the concept of holistic hemodialysis patient care (HHPC) might be proved.

One-third of stroke survivors fail to regain independent ambulation and strokes have been identified as a significant source of long-term disability and a tremendous health burden. Robot-assisted gait rehabilitation is gaining traction and advocators for its inclusion as part of the routine post-stroke rehabilitation program are on the increase. However, despite the recent technological advances in the development and design of better robotics, the research evidence on the best model of robotic training remains sparse and unclear. It is therefore the aim of the current study to comparatively investigate the clinical feasibility and efficacy of a recently developed HIWIN Robotic Gait Training System (MRG-P100) combined with the use of a lab-developed MBS-E100 EMG system as a controller on facilitating the development of an appropriate gait pattern for motor impaired subacute stroke patients. The results indicated that due to the heterogeneity of stroke-induced changes in muscle characteristics, an “auto-fit” algorithm was required to allow constant monitoring and updating of the appropriate threshold based on EMG signals captured during previous gait cycle in order to determine the desired muscle activation threshold for the current gait cycle. Eighteen participants were tested using the new auto-fit algorithm and results demonstrated a significantly more fluent and physiologically appropriate gait pattern.

Digital fringe projection technique is widely used in industrial applications with high accuracy and measurement speed. In this study, a fully automatic high-speed digital fringe projection technique is presented to profile 3D facial characteristics. The structured light with fringe pattern is used to be the light source in the measurement system and is projected by a digital light processing projector. The distorted fringe patterns from facial surface are captured by the digital camera. The absolute phase maps are calculated by using phase-shifting and quality guided path unwrapping algorithm. A complete, 3D facial feature is obtained by our measurement. We achieved simultaneous phase acquisition, reconstruction and three-dimensional (3D) exhibition at a speed of 0.5s. This technique may provide a high accuracy and real-time 3D facial measurement for biometric verification.

The rotational motion has been utilized in several medical needle technologies to enhance the capability of cutting tissue. The needle rotation helps significantly reduce the tissue cutting force, which improves procedure outcome and pain. However, the needle rotation can also incur tissue winding that intensifies tissue damage, which results in complications of bleeding and hematoma. Some histological observations showed that bidirectional needle rotation could reduce the tissue damage caused by tissue winding. In this study, we established a cohesive surface based finite element model to evaluate the cutting force in needle insertion with unidirectional and bidirectional rotation. The simulation results suggested that the frequency of switching direction of needle rotation insignificantly influences the cutting force. The Latin Hypercube method was used to generate a response surface of cutting force and locate the minimum at the insertion speed of 1mm/s combined with the slice/push ratio of 1.9. In clinical use, we suggested that the needle speeds can be first selected to optimize the cutting force according to the type of target tissue. If the desired needle rotation is high, a proper switching frequency can be applied to reduce the tissue winding damage without increasing the cutting force.

In this paper, the wrist braces for the wrist fracture patients are developed. Geometry of the patient’s wrist surface anatomy was digitalized and recorded by an optical 3D scanner. An expert software was developed to generate the brace model, on which several holes are distributed to increase the air permeability. Finally, the brace is fabricated by commercial FDM 3D printer. For ensuring the strength of the wrist brace, the tensile test and impact test were conducted to measure the elastic modulus, yielding strength and fracture strength. A finite element model was established to investigate the stresses and deformations when the wrist brace is subjected to a static load. The mechanical properties measured in the tensile tests are as input parameters in the model. The static analysis showed that, for four considered movements of the wrist, the maximum von-Mises stress is less than the yielding strength. An impact analysis was also conducted to simulate brace impacted by a moving rigid ball with a mass of 0.3768kg. The results showed that the deformation at the impact point remains in the elastic range when the impact speed is 3m/s. The finite element calculations give us rules to design the number of holes and the thickness of the brace.

Dynamic hip screw (DHS) is commonly used for stable-type intertrochanteric hip fractures. The importance of lateral femoral wall has been mentioned while treating intertrochanteric hip fractures with DHS. The aim of this study was mainly to investigate the biomechanical effect of different thickness of lateral femoral wall using finite element analysis (FEA). This study constructed FEA simulation models for five different lateral femoral wall thicknesses, and demonstrated the stress distribution on the femoral bone, the cortical screws, the cancellous bone around the lag screw, and the lag screw. The main results showed that when the DHS is implanted, less stress will be distributed at the implantation site on the femur due to the stress-shielding effect. The stress on the cortical screws will be greater at the junction of the cortical screws and the cortical bone. Intertrochanteric hip fractures with a thinner lateral wall thickness may cause higher stress on the femur after DHS is implanted.

Multiple variables have been shown to influence early marginal bone loss around dental implants. Among these factors, the location of the microgap related to the alveolar crest, occlusion, crest module and soft tissue thickness were reported to be important factors for deciding the final outcome of the implant treatment. The purpose of this study was to establish a damping model to simulate the mechanical function of dental implants in the oral cavity. The experimental implant model consisted of a screw-type implant (10mm). The implant was placed into epoxy resin which was used to simulate bone tissue. In this study, two kinds of epoxy resin were used: PL-1 (with elastic moduli of 2900MPa) and PL-2 (210MPa) were used to simulate cortical bone and cancellous bone, respectively. Above bone block, a soft lining material was used to simulate the soft tissue around implant. In addition, two-implant model with various distance between implants were established to discuss the effect of soft tissue effect on the damping factors (DF) of the implant system. A noninvasive impulse-forced vibration technique was used to detect the damping factors of the implant models as previous reported. Briefly, the signal excitation was detected through the micro-phone and sent to the spectrum analyzer. The frequency response was obtained from a vibration-time histogram using Fast Fourier Transform software. The DF value of the signal dental implant model was detected to be $0.044\pm 0.009$. This value is closed to the in vivo data that was reported previously. This result showed that the model established in this study is a validated model for damping analysis. Furthermore, the DF value of a dental implant surrounded with 3mm soft tissue ($0.127\pm 0.032$) is significantly higher than the implant with 2mm-surround soft tissue ($0.079\pm 0.013$). In addition, implant models with larger interval distance between implants showed higher DF values. According to the results of this study, it is reasonable to suggest that dental implant surrounded with higher amount soft tissue may reduce more vibration amplitude while an occlusal force was applied to a dental implant. This vibration reducing effect may be helpful to reduce alveolar bone resorption around implants.

Pedicle screw loosening at the bone–screw interface is the main complication in pedicle screw fixation. The transpedicular polymethylmethacrylate screw augmentation technique has recently become the general technique used to re-operatively overcome pedicle screw loosening. This study investigates the fatigue resistance of PMMA bone cement augmentation. Twenty-seven porcine thoracic vertebral bodies were collected. The BMD was measured using dual X-ray absorptiometry. Each vertebral body was instrumented with one pedicle screw and mounted in a material testing system. Fatigue testing was performed by implementing a cranio-caudal sinusoidal, cyclic (5Hz) load. This study shows that transpedicular pedicle screw augmentation with PMMA exhibits similar fatigue resistance as traditional pedicle screw implantation. However, in histomophometrical analysis, the transpedicular pedicle screw augmentation with PMMA has greater anti-deformation capacity than traditional pedicle screw implantation. Transpedicular pedicle screw augmentation with PMMA improves more screw holding power to prevent pedicle screw loosening.

Objective: The aim of this study was to investigate the biomechanics of the facial skeletal for understanding the buttress after fixation with standard and modified anatomical thin titanium mesh (ATTM) plates by finite element (FE) analysis. Methods: Standard ATTM (SATTM) plate designed as the “L”-shape anticipated to be fixed in the ZMC anterior maxilla and lateral buttress to increase the fixation screw anchoring strength and another modified ATTM (MATTM) plate with a protrusion in the medial side and a slot and barb design in the lateral side to enhance the zygomaticomaxillary/nasomaxillary buttresses and provide precise positioning to the ZMC segments were studied by the FE analysis under masticatory forces with 250N. Result: The FE simulation results indicated that the total displacement distribution of the maxillary for ZMC fracture fixation with MATTM plate was smaller than that of SATTM plate. Stress concentration was found at the frontal and alveolar processes of the maxillary bone for SATTM plate fixation. Local vector plots of the first principal stress near the frontal process of the maxillary and zygomaticofacial formen of the zygomatic indicated that the stress flow for MATTM plate fixation was relatively close to nasomaxillary buttress, and the zygomaticomaxillary buttress, respectively. Conclusions: This study concluded that “L”-shape ATTM plate designed with a protrusion in the medial side and a slot and barb design in the lateral side can enhance the zygomaticomaxillary/nasomaxillary buttresses under uniform occlusal condition.

Arthroscopic cartilage regeneration facilitating procedure (ACRFP) has been reported with satisfactory results, yet there is limited research on the biomechanics in these patients. The purpose of this study is to assess the change on the biomechanics after ACRFP, in terms of foot pressure and gait pattern. Patients with chronic knee pain due to osteoarthritis and received ACRFP were recruited, and the knee joints in each patient were divided into either study or control group according to radiographical or symptomatic severity. Assessments were done with Knee injury and Osteoarthritis Outcome Score (KOOS) and dynamic foot pressure at the time before surgery, three months and six months postoperatively. A total of 24 patients completed the study. Significant improvement was found of KOOS, at both three and six months postoperatively. No much change in the gait parameters was noted, but there was a significant decrease of foot pressure over lateral side of hindfoot at six months postoperatively. In conclusion, significant clinical improvements could be achieved with surgical results of ACRFP, and shifting of the foot pressure medially may be related to decrease in the knee adduction moment, which is more favorable for the knee joints.